GLENDALE, Ariz. — Sen. Jeff Flake delivered a stark warning to business leaders eager to learn more about GOP plans to remake the health-care system: It’s really hard, and Republicans might not succeed.

“There are some still saying that we’ll vote before the August break. I have a hard time believing that,” he told about 150 members of the local Chamber of Commerce here this week.

Similarly, when a hospital employee asked about how to save the Medicaid program, Flake said, “We’re trying to find that balance, and we aren’t close yet, frankly.”

Flake (R-Ariz.) isn’t afraid to buck President Trump — or to defy the Republican orthodoxy in Washington that the agenda is proceeding apace. He did it last year, refusing to support Trump for president, and he’s doing it again now by publicly doubting that the GOP can revamp the nation’s health-care system.

Few congressional Republicans go as far as Flake, fearful that pro-Trump forces could derail their reelection campaigns next year. And Flake is already paying his own price, drawing a conservative primary opponent and probably earning him the distinction as the GOP incumbent most vulnerable to an intraparty challenge.

These lawmakers might want to consider crossing the aisle in the 115th Congress

“If I wanted an easier path through the primary, then I would line up more with where the president is,” he said. “But I think if you’re an elected official, you’ve got to do what you know what’s right. It’ll be a tougher path than I could have had, would have had, but I think I’ll get there.”

Flake’s independent streak mirrors that of his fellow Arizona Republican in the Senate — John McCain. And it’s not necessarily out of step with his state: Trump defeated Democrat Hillary Clinton 49 percent to 45 percent — the narrowest win for a Republican since 1996, the last year a Democrat, Bill Clinton, won Arizona.

Yet Flake faces challenges that McCain does not — notably name recognition. Polling is scant in Arizona, but a survey last fall gave Flake a 35 percent favorability rating, with roughly 30 percent of voters unwilling or unable to render an opinion of him.

In appearances across Phoenix this week, Flake focused on tempering expectations.

Like other Republicans, he wants to drive down health-care costs for consumers, many of whom in Arizona, he said, are spending more each month on health care than their mortgages. But more than a quarter of Arizonans get health-care coverage from Medicaid, leaving many here vulnerable to Trump’s proposed $1.4 trillion in cuts to future spending on the program — cuts that many Republicans support.

Known as a fiscal conservative eager to slash Medicaid and other entitlements, Flake said he supports the cuts, but only if governors can take more control of the program and if the program remains “sustainable” so that beneficiaries “don’t have the rug pulled out from under them.”

That’s a tricky balance to strike. Flake faces reelection next year in a state where Democrats are making gains, and Republicans may want him to take a harder line on repealing the Affordable Care Act. Defending just eight seats next year, the GOP isn’t expected to lose control of the Senate, but Flake and Sen. Dean Heller (R-Nev.) are expected to earn outsize attention from Democrats, who know that these Western states are increasingly tilting purple or blue.

Flake tours the Palo Verde nuclear power plant in Tonopah, Ariz., before holding a town hall with employees Tuesday. (Caitlin O’Hara/The Washington Post)

Meanwhile, Kelli Ward, Flake’s conservative opponent, called his refusal to support Trump last year “treacherous” and criticized him for standing against the president “before Donald Trump became the nominee, after he became the nominee and after he became the president.”

She also warned that nothing short of a full repeal of Obamacare would be acceptable to many GOP voters.

“I wish that over the last seven years that they had been planning for the full repeal that they campaigned on and fundraised upon,” said Ward, who mounted an unsuccessful challenge against McCain last year.

Flake has mostly ignored Ward’s barbs. He plans to hold fundraisers with Mitt Romney on Friday and has already raised money with George W. Bush — two GOP leaders who cast doubt on Trump. He touts his work with former president Barack Obama to open up diplomatic relations with Cuba. A co-sponsor of the 2013 bipartisan immigration bill, Flake tells audiences that he believes the issue might be debated again later this year. At odds with Trump’s nationalist tendencies, he said Tuesday that “we’re all better off because of” globalization and that NAFTA should be renegotiated, not scrapped. And he insists that the only way to fix health care is with bipartisan consensus.

“Some are saying: ‘Stand on principle, don’t deal with the other side, just ram it through, they did it when they were in charge.’ But then you have others that say you need to work with the other side, that’s the only way it can be done,” Flake said. “There’s push and pull everywhere. You just do the best you can.”

Flake, 54, grew up in Snowflake, Ariz., a town named for his great-great-grandfather. Flake served as a Mormon missionary in South Africa in the 1980s before finding his way to Washington to work at a public relations firm. He moved back to Arizona as head of the Goldwater Institute and won a House seat in 2000. His perpetual tan and Jimmy Stewart demeanor earned him national attention when he escaped alone to a deserted island in the Pacific Ocean during a 2009 congressional recess.

In 2012, Flake won his Senate seat and now serves in the long shadow of the state’s senior senator, McCain. During a stop Tuesday at the Palo Verde nuclear power plant in Tonopah, Ariz., Flake told workers that on a recent flight home to Phoenix on a plane that was also carrying McCain, he sat next to a woman who had no idea he also serves in Congress.

“The guy sitting in front of me finally leaned back and said, ‘Hey lady, he’s the OTHER senator from Arizona!’ ” Flake said.

Updating the workers on events in Washington, Flake lamented that after years of congressional gridlock, “We haven’t regulated the regulators,” allowing federal agencies to impose what he considers burdensome policies on the energy sector and other industries. He explained that “the Senate is kind of in the personnel business,” stuck confirming hundreds of Trump administration appointees. He said that Trump “has assembled a pretty good Cabinet. He’s surrounded himself with a good group of people.”

But he was more critical of Trump during a private tour of the plant. Riding in a van to inspect a nuclear waste site and reactor, Flake heard pleas to ensure that Kristine L. Svinicki, chairman of the Nuclear Regulatory Commission, gets reappointed before her term expires at the end of June. If her term ends, the agency that regulates nuclear power would be paralyzed without a quorum.

Flake told Donald Brandt, the plant’s chief executive, and Robbie Aiken, its Washington-based government affairs vice president, that he believes that Democratic objections to Trump nominees will start to ease as the Senate moves to confirming deputy secretaries and less controversial appointees. But he said that Trump owes Congress hundreds of nominees for political jobs.

“We can’t hold oversight hearings because we can’t call anybody up to testify,” he said.